Demountable filament assembly



I April 17, 1956 w. J. ARMSTRONG ETAL 2,742,587

DEMOUNTABLE FILAMENT ASSEMBLY 2 SheetsSheet 1 Filed July 11, 1952 A ril17, 1956 w 1. ARMSTRONG ETAL 2,742,537

DEMOUNTABLE FILAMENT ASSEMBLY Filed July 11, 1952 2 Sheets-Sheet 2William J. Armstrong, Paul I. Corbell, and'Kenneth H. McPhee, CedarRapids, Iowa, assignomby mesne assignments, to the United States ofAmerica as represented by the United States Atomic Energy CommissionApplication July 11, 1952, Serial No. 298,262 4 Claims. (Cl. 313-473)This invention relates in general to filaments for electron tubes, andin particular to filaments of extremely high current capacity for tubesof the resnatron type where the average power may be as high asSOkilowatts.

The development of electronics has led to the design of higher andhigher poweredtubes until presently, tubes are being built whichdevelope 50 kilowatts average power. With such large tubes, extremelylarge cathode current is required and the extreme heat generated by suchcathodes rnust be removed so as to prevent the internal elements of thetube from melting. v

The present invention comprises a high current filament which ismaintained cool enough to prevent injury to the filament and in whichthe active elements of the assembly are prevented from bowing or beingdeflected.

Further objects, features and advantages of this invention will becomeapparent from the following description and claims when read in view ofthe drawings, in which:

Figure 1 is a view of the filament assembly of this invention withone-quarter of the assembly removed to' show the internal construction,

Figure 2 is a detailed view of the filamentand supporting portion, and

Figure 3 is the detailed view of the pantograph of the invention.

The active portions 19 of the filament eittend upwardly i to an uppersupporting assembly designated generally as 20 and which is attached tothe upper cylinder 11.

The upper supporting assembly is shown in detail in Figure 2. An endcover plate 21 covers the lower end of the cylinder 11 and extendsoutwardly therefrom to form a heat shield flange 22. A second collar 23is mounted between the lower end of the cylinder 11 and the plate 21 andis formed with an opening through which a bolt 24 passes. The boltpasses through a stainless steel ring 27 which rests on the plate 21.The head 26 of the bolt engages the ring 27.

The upper end of the bolt passes through one end of a pantographassembly 28 and a nut 29 is received thereon to clamp the pantographassembly together. The pantograph assembly 28 comprises a plurality offlexible heat and electrical conducting members formed in the mannershown in Figure 3.

Copper strips 30 have each end folded under to form ,spacers so that thecenter portions will be free to slip relative to' each other. One end ofthe pantograph assembly is formed with an opening 31 through which thebolt 24 passes and the other end is formed with a pair UnitedStatesPatent ICC Patented Apr. 17,. 1956' of openings 32 and33th'roughwhich bolts 34"and 35 pass. The lower ends of bolts 34 and 35are threadedly received in a block which supports the upper end 37 ofthe filament ,19. A bolt 38 is received in the block 36 and a nut 39clamps'the'upper end of the filament to the block. I

A block 40 is mounted to the upper endof the pantograph and bolts 34 and35 pass'therethrough. Holding nuts 41 ands42-clamp theiblock'4ll tothe'pa'ntograph assembly. Y A pair of annular brackets 43 and 44 extendoutwardly from the cylinder wall llabove the pantograph ,assem blyandare formed with-axial aligned openings 45 and 46. A threaded sleeve 47threadedlyreceives'the upper end'of'the bolt 35 therein and passes upthrough the opening 45. A threaded pin 48 extends through the opening 46and is threadedly received in the collar 47. The pin 48 carries'ashoulder 49 which'engages the upper end of a spring 50 which is clampedbetween the upper portion of the member 43 and the shoulder 49. Theupper end of the pin '48 is'forme'd with a slot 51 into which a screwdriver may be inserted for adjusting the tension of the spring.

7 Due to the extremely high temperatures developed during operation ofthe filament, which might be 2700 Kelvin for the active portions 19, itis necessary that a large amount of heat be transferred through thepantograph assembly 28.

The nuts 29, 39, 41 and 42 are made of stainless steel 1 which it ismounted. Kovar is an alloy which has the same coeflicient of thermalexpansion as glass, and comprises from 28 to 30 percent nickel; 15 to 18percent cobelt; and the remainder iron. Thus, when subjected 'toheating, the bolt 38 and nut 39 will have a tightening effect on theendof the filament 19. This prevents a bad contact between the filamentand the block.

The spring 50 might be made of tungsten which has a high resistivity toheat so that its tension will not 'be substantially decreased whenheated.

Applicant has built a tube which uses a filament assembly such, asshown'in Figure 1 wherein the active tungsten filaments 19 are 6 inchesin length, one-quarter inch wide, and 0.040 inch thick. Thirty-sixfilaments are mounted about the circumference. Each filament draws 350amperes and the total heating current is 12,000 amperes at 5 volts, 60cycle A. C. The total power for heating is near 60,000 watts. Thefilament has passed nutensionwhich might be approximately 10 pounds sothat a it is not deflected when heated due to thermal expansion andgrain growth, and it also is not displaced relative to the center lineof the filament assembly. The action of the pantograph assembly 28 givesa parallel motion upwardly with the transverse motion being very small.This maintains a symmetry 'ofthe filament assembly and does notsubstantially increase the cathode to plate distance.

. Although the invention has been described with respect to particularembodiments thereof, it is no to be so limited as changes andmodifications may be made therein which are within the full intendedscope of the invention, as defined by the appended claims.

We claim:

1. A filament basket comprising a lower supporting cylinder, an uppersupporting cylinder, a plurality of filaments with their lower endsattached to the lower supporting cylinder, a plurality of blocks eachconnected to the upper end of one of said filaments, a pair of annular 3brackets attached to the upper supporting cylinder, a plurality ofsleeves each connected to one of said blocks and each passing up throughan aligned opening formed in one of the brackets, and a spring mountedover each of said sleeves and engaged withone of said brackets to placethe individual filaments under tension.

2. Filament tension means comprising, a lower supportingrmember, anupper supporting member, a filament with its lower end attached to thelower supporting member, a plurality of sheets of flexible materialconnected to said upper supporting member, a block attached to the upperend of said filament, said sheets attached to said block, a bracketattached to said upper supporting member, a sleeve threadedly connectedto said sheets and extending through an opening formed in'said bracket,and a spring biasing means urging said sleeve member upwardly.

3. A filament assembly comprising, a lower supporting cylinder, an uppersupporting cylinder, a plurality of filaments with their lower endsattached to the lower supporting cylinder, a plurality of'blocks, theupper ends of said filaments attached to said blocks, a plurality ofassemblies of sheets of flexible material, one end of each assembly ofsheets attached to the upper supporting cylinder, the other end of eachof said assembly of sheets attached to said blocks, a bracket generallyannular in shape passing around said upper supporting cylinder abovesaid sheets, and a plurality of spring biasing means passing throughsaid bracket and engaging said sheets to maintain the filaments undertension.

4. Filament tensioning means comprising, a lower cylinder, an uppercylinder, a plurality of filaments with their lower ends attached to thelower cylinder, a plurality of blocks connected to the upper ends ofsaid filaments, a plurality of flexible sheet assemblies, one end ofeach of said assemblies connected to the upper cylinder member and theouter ends connected to said blocks, a pair of annular brackets mountedto said upper cylindrical member above said assemblies, a plurality oflead screws extending upwardly from said blocks, collars threadedlyreceived on each of said lead screws, a second plurality of lead screwsthreadedly received in said collars and each formed with a shoulder, anda spring mounted between each of said shoulders and said first bracket.

References Cited in the file of this patent UNITED STATES PATENTS

